The effect of phenological asynchrony on population dynamics: analysis of fluctuations of British macrolepidoptera

Experimental studies have shown that changes in plant chemistry due to host-plant phenological development can affect insect growth, survival, development and fecundity. It has therefore been hypothesised that phenological asynchrony is responsible for large density-independent fluctuations in insect abundance from year to year. However, there is little direct evidence to support this hypothesis. The aim of this study was to assess the importance of phenological synchrony by testing the hypothesis that moths that commence feeding on tree foliage early in the growing season of their host plants are likely to show greater fluctuations in abundance than species feeding later in the year, because the former are more susceptible to phenological asynchrony. Data on the abundance of 81 British macrolepidoptera were obtained from the Rothamsted Insect Survey light-trapping net,work, Each species,vas classified according to the month when their larvae commenced feeding and the population variability of each species was estimated using both the population standard deviations (SD (log(N + 1)), where N equals population size) and the coefficient of variation (CM. Population variability did not vary significantly between moths whose larvae emerged on different months. Polyphagous moths fluctuated less than monophagous species and the timing of the beginning of the adult flight period has found to affect population variability as measured by SD (log(N + 1)). (In all other cases similar results were obtained from both measures of population variability.) Population variability,vas greatest among species whose flight periods started in February and April, and lon est among those flying in Ma) and September. This analysis therefore provided no evidence to support the hypothesis that phenological asynchrony has a major impact on the abundance of tree-dwelling insects. Comparative patterns in the variability in abundance of tree-dwelling moths may relate more to direct effects of climatological factors than indirect, host-plant mediated effects, such as phenological asynchrony.